Fahim M.A., Sahhaf T.A., Elkilani A.S. Fundamentals of Petroleum Refining
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Point Source Discharge In the petroleum refining industry, the dissolved
organic carbon (DOC) of refinery effluents is a known parameter. Hence,
the emission factors for organic compounds in Table 17.11 are based on the
DOC. Trace elements and inorganic compound emissions factors are also
expressed in Table 17.11.
Table 17.10 Typical refinery waste water effluents before treatment (CONCAWE, 1999)
Oil H
2
SNH
3
Phenols TOC CN- TSS
Distillation XX XX XX X XX – XX
Hydrotreater XX XXX XXX – XX – –
Visbreaker XX XX XX XX XX X X
FCC XX XXX XXX XX XX X X
Hydrocracker XX XXX XXX – X – –
X < 50 mg/l; 50 < XX < 500 mg/l; XXX > 500 mg/l. TOC is total organic carbon.
Table 17.11 Typical emissions in refinery effluent (Ontario Ministry of Environment, 1994)
Component wt% of DOC
Toluene 9.2 10
4
Benzene 9.1 10
4
Xylene 1.4 10
3
Phenol 6.9 10
4
1,2-Dichloroethane 2.7 10
4
Hexachlorohexane 4.4 10
4
PAH 1.6 10
3
Styrene 1.0 10
4
Ethylbenzene 1.2 10
4
1,1,2-Trichloroethane 3.6 10
3
Chloroform 2.5 10
3
Elements Emission factor (kg/m
3
)
Zinc 4.4 10
4
Phosphorous 4.1 10
7
Arsenic 6.7 10
6
Chromium 7.7 10
6
Selenium 3.1 10
6
Nickel 3.6 10
6
Copper 2.9 10
6
Antimony 5.8 10
7
Cobalt 1.6 10
6
Mercury 1.1 10
8
Cadmium 3.3 10
7
Lead 1.9 10
6
Cyanide 1.3 10
6
446 Chapter 17
These factors are applied to the following effluent parameter:
WWE ¼ DOCðwt%=100ÞðFlowÞð17:15Þ
where WWE is the wastewater emission of a component from the treat-
ment plant (kg/h), DOC is the dissolved organic carbon of the treated
effluent discharged (kg/m
3
), wt% is the weight percent of the component as
provided in Table 17.11, and Flow is the wastewater flow rate discharged to
the receiving body of water (m
3
/h).
Example E17.10
Calculate the benzene and nickel emission rates from 1000 m
3
/h typical refinery
wastewater effluent. A typical DOC in this effluent is 0.1 kg/m
3
.
Solution:
From Table 17.11, for benzene DOC wt% ¼ 9.1 10
4
Benzene emission rate ¼ (0.1 kg/m
3
) (9.1 10
4
/100) (1000 m
3
/h) ¼ 9.1
10
4
kg/h
Nickel emission rate ¼ (1000 m
3
/h) (3.6 10
6
kg/m
3
) ¼ 3.6 10
3
kg/h
Example E17.11
The effluent wash water in a desalter will contain salts removed from the crude
oil. Calculate the effluent salt content of the effluent, considering the following
operating conditions:
Crude oil ¼ 25,000 BPD
Inlet salt content ¼ 100 lb/1000 bbl
Outlet salt content in crude ¼ 3 lb/1000 bbl
Outlet water content in crude ¼ 0.3 vol%
Water in crude oil ¼ 0.5 vol%
Wash water ¼ 5 vol% on crude
Solution:
Salt removed ¼ 100 3 ¼ 97 lb/1000 bbl
¼ 97 (25) ¼ 2430 lb/day
Effluent water ¼ (0.05 þ 0.003) (25,000) ¼ 1325 bbl/day
¼ (1325 bbl/day) (42 gal/bbl) (35.3145 ft
3
/264.17 gal) (62 lb/ft
3
)
¼ 463,000 lb/day
Salt in effluent water ¼ (2430 lb/day)/(463,000 lb/day) (100) ¼ 0.53 wt%
¼ 5300 ppm
Environmental Aspects in Refining 447
Example E17.12
10,000 BPD of 30 API crude oil and a wash water rate of 5 vol% on the crude
are used in a desalter. T he crude oil contains 100 ppm of sulphides and the wash
water contains 100 ppm of sulphides. Using a water/oil partition coefficient of
4, calculate the sulphide concentration in the wash water effluent.
Solution:
Crude oil of 30 API ¼ 10,000 BPD ¼ 128,000 lb/h
Wash water used ¼ 0.05 (10,000 bbl/day) (42 gal/bbl) (35.3145 ft
3
/264.17 gal)
(62 lb/ft
3
) (day/24 h) ¼ 7252 lb/h
Total sulphides entering the process ¼ [100 10
6
(128,000) þ 100 10
6
(7252)]
¼ 13.525 lb/h
Let x be the sulphide content in effluent water and the water oil partition
coefficient equal 4 then,
4 ¼
sulfide in water
sulfide in oil
¼
ðx=7252Þ
ð13:525 xÞ=128; 000
gives x ¼ 2:5lb= hr
The sulphides concentration in the wash water effluent ¼ (2.5/(7252)) (10
6
) ¼
345 ppm
17.3.2.2. Treatment and Control
Petroleum refineries typically utilize primary and secondary wastewater
treatments. Table 17.12 shows typical effluents after treatment.
Table 17.12 Typical water effluent composition (World Bank, 1996; USEPA, 1995)
Primary
treatment
effluent
composition
(mg/l)
Secondary
treatment
effluent
composition
(mg/l)
USEPA
standard
emissions
(kg/day)
Oil 40 0.05–9.8 99
Chemical oxygen demand (COD) 300 30–225 2371
Biological oxygen demand (BOD) 150 2–50 338
Total suspended solids (TSS) 10–20 2–8 270
Phenols 12 0.03–1.0 2.1
Sulphide 5 0.01–1.0 1.8
MTBE 0–3 <1
PAH 0.1 0.005–0.05
BTX 5 <0.001
Metals 1 0.1–1.0
448 Chapter 17
Primary Treatment Primary treatment is the separation of hydrocarbons
from wastewater. API separators gravity separation and settling chambers
remove suspended hydrocarbons, oily sludge and solids by gravity separa-
tion, skimming and filtration. Some oil–water emulsions must be heated to
assist in separating the oil and water. Acidic wastewater is neutralized using
ammonia or soda ash. Alkaline wastewater is treated with sulphuric acid,
carbon dioxide-rich flue gas or sulphur. Figure 17.3 shows a schematic
diagram of API separator.
Secondary Treatment Oily water is segregated into two streams: low
(160–250 ppm) and high oil content (>250 ppm). The low stream is
made up primarily of stripped sour water and requires no further treatment.
A high oil stream is treated using API oil/water separator followed by
dissolved air floatation (DAF) separator.
Activated carbon is used to remove heavy hydrocarbons from light
organic gas streams in the refinery. Furthermore, by using a catalyst com-
bined with hydrogen peroxide, it is possible to reduce the chemical oxygen
demand (COD) and the biological oxygen demand (BOD). Besides, phe-
nols are transformed into less biodegradable compounds which can be
removed by subsequent coagulation and precipitation. Removal of soluble
and insoluble organic and inorganic contaminants from refinery wastewater
streams is performed by employing ultra-filtration and membrane
separation.
The high oil content water goes into a second stage, which utilizes
physical or chemical methods to separate emulsified oils from the wastewa-
ter. Physical methods include settling ponds with a long retention time. In
DAF, air is bubbled through the wastewater, and both oil and suspended
solids are skimmed off the top. Chemicals, such as ferric hydroxide or
aluminium hydroxide, can be used to coagulate impurities into sludge,
which can be more easily skimmed off the top. Table 17.13 shows the
influent and effluent data for API and DAF processes.
Raw water
Sludge
Decanted
water
Oils
Figure 17.3 Schematic diagram of API separator
Environmental Aspects in Refining 449
Tertiary Treatment Operations These treatments include chlorination,
ozonation, ion exchange and activated carbon adsorption. Compressed
oxygen is diffused into wastewater streams to oxidize certain chemicals or
to satisfy regulatory oxygen-content requirements. Wastewater that is to be
recycled may require cooling to remove heat and/or oxidation by spraying
or air stripping to remove any remaining phenols, nitrates and ammonia.
Figure 17.4 summarizes the wastewater schemes through primary,
secondary and tertiary treatment.
Table 17.13 Typical operating data for secondary treatment (Parakash, 2003)
API DAF
Inf luent Effluent Influent Effluent
TSS (ppm) 500 500 500 20
Total oil (ppm) 410 180 21,640 13
COD (ppm) 1000 500 640 300
BOD (ppm) 620 310 320 150
Phenols (ppm) 3 3 3 1.8
Sulphides (ppm) 10 10 10 8
Tank
Farm
Drainage
Refinery
Process
Units
Sour
Water
Stripper
Desalter
Surge
Pond
API
Separator
Air
Floatation
Oil
Tra p
Cooling
Tow er
Blow
Equalizing
Basin
Biological
Treating
Ter ti ar y
Treatment
Final
Pond
Boiler
Blow
down
Clean
Discharge
Figure 17.4 Typical refinery wastewater system
450 Chapter 17
Example E17.14
A sour water at 37
C and 275 kPa is heated to 93.3
C and then stripped in a
column to separate H
2
S and NH
3
from wat er. Sour water contains 0.7 mol%
H
2
S and 0.5 mol% NH
3
, and the balance is water. The feed flow is 331.22 m
3
/
h. The heat exchanger uses stripped water from the column in the shell side to
heat the sour water feed which enters the heat exchanger tube side. The
preliminary specifications for the column are a reflux ratio of 10 and the
ammonia at the reboiler is 10
5
mol fraction. Use UNISIM simulator to do
the material balance for all streams (UNISIM, 2007).
Solution:
Figure E17.14 shows a simplified flow chart for the process. Table E17.14
summarizes the material balance and operating conditions.
Off Gas
Stripper Feed
Sour
Water
Stripper
Sour
Water
Stripper
Bottoms
Heat
Exchanger
Effluent
Figure E17.14 Sour-water treatment
Table E17.14 Summary of results
Sour
water Effluent
Stripped
feed Off gas
Stripped
bottoms
H
2
S mol% 0.7 0 0.3712 16.95 0
NH
3
mol% 0.5 0.001 0.5305 24.18 0.001
H
2
O mol% 98.8 99.999 99.0983 58.87 99.999
Temperature (
C) 37.8 67.8 93.3 105.4 124
Pressure (kPa) 275.8 156.5 206.8 197.9 225.5
Flow (m
3
/h) 331.22 321.4 331.22 9.82 321.4
Environmental Aspects in Refining 451
17.3.3. Solid Waste
Refinery solid wastes are typically in the form of sludge, spent process
catalysts, filter clay and incinerator ash. Sludge is generated from the gravi-
tational separation of oil/water/solids during the storage or treatment of
process wastewaters. It is also generated from cooling waters segregated for
treatment from other process or oily cooling waters. Storage tank bottoms
are mixtures of iron rust from corrosion, sand, water, emulsified oil and
wax, which accumulate at the bottom of tanks. Tank bottom sludge is
removed during the periodic cleaning of tanks for inspection.
Both hazardous and non-hazardous solid wastes are generated, treated
and disposed. Treatment of these wastes includes incineration, land treating
off-site, land filling on-site, land filling off-site and other treatment meth-
ods. Figure 17.5 shows the refinery sludge paths. Table 17.14 shows typical
sludge and solid waste in refinery units.
Stabilization
1.5%
Pretreatment
75%
After Stabilization
2%
Sludge for disposal
100%
After pretreatment
16.8%
Alternate fuel use
3.8%
Unidentified
0.7%
Incineration with
energy recovery
27.9%
Incineration without
energy recovery
16.1%
Land farming
8.7%
Other techniques
13.5%
Landfill
29.3%
Raw Sludge
100%
No Treatment
23.5%
Figure 17.5 Refinery sludge routes (CONCAWE,1999)
452 Chapter 17
The toxicity and amount of de-oiled and de-watered sludge is reduced
through thermal treatment. Thermal sludge treatment units use heat to
vaporize the water and volatile components in the feed and leave behind a
dry solid residue. The vapours are condensed for separation into hydrocarbon
and water components. Non-condensable vapours are either flared or sent to
the refinery amine unit for treatment and then used as refinery fuel gas.
Questions and Problems
17.1. Fuel containing 3 wt% sulphur is burned in a furnace to heat crude
before introducing it to the crude distillation unit. Calculate the
amount of SO
2
emitted form the furnace stack per 1000 kg fuel
burned. Calculate the amount of air required for combustion.
Table 17.14 Solid waste percentages in refinery processes
(CONCAWE, 1999)
Type of waste wt%
Sludge
API/DAF 41.8
Wastewater bio-treatment 30.2
Boiling fresh water 13.0
Tank bottom 7.2
Miscellaneous 6.7
Desalter 0.8
Acid alkylation 0.3
Other solid was te
Contaminated soil 26.3
FCC catalyst 19.4
Other wastes 15.5
Miscellaneous oily waste 8.9
Incinerator ash 6.0
Spent caustic 6.0
Other catalysts 4.7
Desulphurization catalyst 3.2
Spent clay 2.7
Tank scales 2.4
Sorbents 1.9
Flue gas desulphurization 1.3
Spent chemicals 1.2
Reformer catalyst 0.4
Acid tar 0.2
Environmental Aspects in Refining 453
17.2. 10,000 BPD crude oil is fed to the crude distillation unit. Fuel
containing 3 wt% sulphur is burned in a furnace to heat that crude
before introducing it to the CDU. Calculate the amount of SO
2
emitted from the furnace stack using the emission factors.
17.3. 70,000 BPD is fed to FCC unit. The regenerator of spent catalyst flue
gas has some amount of escape catalyst. Calculate that amount of
particulate and all flue gas emissions such as CO, SO
2
and others.
17.4. 100 kg/h fuel contains the mole % of gases shown in the low-pressure
flare gas in Table 17.6. It is burned in a flare. Calculate the CO
2
emission rate based on a material balance and on emission factors
listed in Table 17.7 and compare.
17.5. It is ascertained that 200 valves are with 90 wt% (non-methane
hydrocarbons) and 10 wt% methane in a pipeline of a plant. Valves
operate for 5000 h/year. Calculate the fugitive emission rate.
17.6. 1000 kg/h fuel is burned in a furnace with 95% efficiency. The fuel
contains 2.5 wt% sulphur. The furnace stack is 50 m high. If there is a
residential area about 1 km downwind from the stack, calculate the
amount of SO
2
that reaches the residential area at a day of 3 m/s wind.
17.7. Solve example E17.8 by hand calculation and compare with the
UNISIM results.
17.8. ESP with a plates spacing of 25 cm is attached to 50 kV of electric
power. The dirty gas flows at 2 m/s and carries particulates with
0.4 mm at 100
C. Calculate the plate length to capture 98% of the
particulates.
17.9. Calculate the phenol and lead flow rates from 1000 m
3
/h typical
refinery wastewater effluent. A typical DOC in this effluent is
0.2 kg/m
3
.
17.10. The effluent wash water in a desalter will contain salts removed from
the crude oil. Calculate the effluent salt content of the effluent consid-
ering the following operating conditions:
Crude oil ¼ 50,000 BPD
Inlet salt content ¼ 100 lb/1000 bbl
Outlet salt content in crude ¼ 5 lb/1000 bbl
Outlet water content in crude ¼ 0.2 vol%
Water in crude oil ¼ 0.5 vol%
Wash water ¼ 5 vol% on crude
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454 Chapter 17
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Environmental Aspects in Refining 455